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Mustek DVD, logic is dead

Discussion in 'Electronic Repair' started by Stefan Toftevall, Dec 23, 2003.

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  1. Hi all,
    I got a Mustek DVD player into my repair shop some days ago. The
    customer told me the unit was all dead. TRUE!
    A fast examination of the smps revealed a shorted zener diode in the
    primary part of the supply (a 15V zener used as transient surpression
    on the switching FET's gate to ground).
    Ok, I replaced the zener and the smps now operates perfect generating
    all its secondary voltages.
    BUT, the player is STILL DEAD! The mainboard gets all the power it
    should and so does the display board, but there is absolutely NO
    response from the logic.
    This tells me, either some sort of Power on reset pulse is missing, or
    otherwise the microcontroller is blown. Though, I still believe I
    should have at least something light up or the standby/power on led
    light up.
    Maybe some of you have faced the same problem somewhere,
    Any advice is appreciated!
  2. James Sweet

    James Sweet Guest

    Is there a surface mount fuse anywhere on the logic board? Perhaps the power
    supply's voltage shot way up and blew it. The micro could also easily be
    dead if the voltage went up.

  3. Hi James,
    I don't really think the smps got out of regulation and output
    excessive voltages, maybe some nearby thunder light storm caused nasty
    spikes on the mains and caused the 15v clamp zener to short. Its mains
    fuse were also open though it didn't "looked blown", more like it
    opened softly.
    I'll go check the board for surface mount fuses and protectors.
    Thanks for the tip.


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